1. The Field of the Invention:
The present invention is concerned with a hot melt adhesive composition in the form of a stick which may be melted and dispensed from a hot melt glue gun.
2. Description of the Prior Art:
Hot melt glue guns are becoming increasingly popular in various trades and with "Do-It-Yourself" enthusiasts. Examples of glue guns adapted to be held in the hand of an operator and used to dispense hot melt adhesives are shown in UK Patent Specification No. 1402648, and UK Registered Design Application No. 1009681.
In general, it is well known to provide glue guns adapted to be held in the hand of an operator with a melt chamber in which an end portion of a stick is received and melted by heat supplied to the melt chamber. Progressive melting of the glue stick may be achieved by pressing the glue stick into the melt chamber by means of the operator's thumb or a mechanical feed mechanism. Melted adhesive is dispensed from a nozzle of the gun as the stick is fed into the melt chamber and melted therein.
It is one practice to arrange that the melt chamber of such a gun is heated to such an extent that the melt chamber has a temperature in the region of 200.degree. C. during normal operation, although it is known that the temperature of the melt chamber often varies between about 185.degree. C. and 215.degree. C., depending on the rate of dispensing adhesive. It is a practice to employ for the material of glue sticks, compositions based on ethylene vinyl acetate copolymer, having a softening range of about 70.degree. C. to 80.degree. C. and a viscosity at 200.degree. C. of about 5,000 to 15,000 mpas.
Whilst adhesive compositions heretofor proposed for use with glue guns as above referred to are generally satisfactory in many respects, we have observed that the bond strengths achieved on substrates formed from certain materials are undesirably low for structural purposes (for example bonds to plasticised pvc, certain metals and wood) or demonstrate an undesirably low heat resistance of the bond for certain uses, or the adhesives demonstrate an undesirably low thermal resistance when molten. Known compositions also suffer from the disadvantage that the time available to the operator in which he may form a satisfactory bond before the adhesive composition has become too viscous or too hard to manipulate satisfactorily is inadequate under some circumstances, especially for the unskilled user.
It is one of the various objects of the present invention to provide an improved hot melt adhesive glue stick.